Semiconductor integrated fuses are utilized in various types of integrated circuit designs and applications. For instance, integrated fuses are utilized as programmable elements with memory devices (e.g., PROMs, SRAMs, etc.), redundancy for logic devices, programmable feature selection, etc. An integrated fuse can be programmed from a low resistance state to a high resistance state by applying an electric current of sufficient magnitude, and for a sufficient amount of time, to thereby heat the fuse to cause a fusing event (i.e., blow the fuse).
Currently, integrated circuit devices are being developed with higher degrees of integration with decreasing critical dimensions to enable low power applications. In this regard, the required internal power supply voltages and currents that are needed are becoming increasingly smaller. With smaller voltages/currents, however, it becomes more difficult to reliably blow fuses such as polysilicon fuses. Accordingly, integrated fuses structures are being developed to allow fuses to be programmed with reduced currents/voltages.
FIG. 1 is a schematic top plan layout (shape) of a conventional integrated fuse device. In particular, FIG. 1 depicts an integrated polysilicon fuse (10) which comprises a fuse link (11) of length LF and width WF, which is connected between an anode (12) and a cathode (13). The polysilicon fuse (10) can be formed by patterning a polysilicon layer formed on a substrate and doping the polysilicon layer with N-type (N+) or P-type (P+) dopants, for example.
To enable programming at decreased currents/voltages, the polysilicon fuse (10) is designed such that a width WF of the fuse element (11) is made significantly smaller than the widths WC of the anode and cathode regions (12) and (13). The smaller width fuse link (11) provides a high resistance path between the anode and cathode (12) and (13), and the reduction in cross-sectional area between the anode (12)/cathode (13) and the fuse link (11) creates what is known as “current crowding”. This effect is depicted in FIG. 1, where current (15) flowing from the larger area cathode (13) to the smaller area fuse link (11) causes current crowding at the region where the fuse link (11) interfaces to the cathode (13), when a bias is applied to program the fuse. The current crowding effect together with the increased resistance of the fuse link provides an increase in localized heating, which causes the fuse to open with smaller voltages and currents. Although this design generally allows for programming with reduced current/voltage, the fusing location can vary across fuses of similar structure, thus reducing programming reliability.